The manufacture of semiconductor devices is a time consuming process that requires high levels of cleanliness throughout the many phases of the manufacturing process. Many steps of manufacturing are conducted in various classes of "clean rooms" having purified air flows to reduce the incidence of airborne particle contaminants to prescribed levels. Clean rooms are typically designated in accordance with the number of permitted contaminants of a prescribed size per cubic foot of airspace. For example, much semiconductor manufacturing is presently conducted in Class 10 clean rooms, which have filtered air flows to permit no more than 10 particles per cubic foot of up to 0.5.mu. in size. Nevertheless, wafers upon which the semiconductor devices are assembled can become contaminated, and therefore rendered defective, by contaminants that are introduced at various process steps. For example, contamination can arise from incomplete cleansing of reagents from the wafer handling apparatus, and the like. The presence of such contaminants can have a catastrophic impact on product yield, notwithstanding an otherwise proper and complete formation of the semiconductor device. Moreover, although the wafers themselves can be properly cleansed of reagents and the like that are used incident to various manufacturing steps, the wafer handling equipment, for a variety of reasons, may not be completely cleansed of the reagents and may therefore serve as source of wafer contamination for subsequent batches of wafers. Unfortunately, the prior art to date has not properly and fully addressed this latter aspect of contamination, and has instead sought to improve product yield by addressing other aspects of semiconductor device manufacture.
Prior efforts to cleanse wafer handling implements have not been entirely compatible with other aspects of device manufacture. For example, one known prior cleansing method within the clean room provided for the use of a pressurized stream of air that was directed at a wafer handling implement such as a wafer cassette or boat. While this cleansing practice was convenient and expedient, it had the unfortunate consequence of creating turbulence in the airflow within the clean room and introducing particulate contaminants into the clean room airstream, which resulted in increased particle contaminant concentrations at other processing stations within the clean room. While the spread of airborne contaminants was rectified by termination of this cleansing regimen, the cleansing regimen itself was not replaced. Therefore, the original problem associated with contaminated wafer handling implements has largely remained uncorrected. Accordingly, there exists in the semiconductor manufacturing industry a need for wafer handling cleansing methods and apparatus which remove particulate contaminants from wafer handling implements such as wafer cassettes and the like prior to their contact with wafers at various stages of manufacture. The provision of such methods and apparatus could reasonably be expected to increase product yield and therefore result in a corresponding increase in manufacturing efficiency.